Field of the Invention
The present invention encompasses, in part, a method and apparatus for lens casting in which two molds, preferably formed of plastic, are interconnected or joined together via a ring to form a mold cavity having substantially the same dimensions of the lens to be formed therein. The invention is further directed to compositions and methods used in lens casting.
Background
The art of casting lenses involves introducing a lens-forming material, such as a monomer or monomer mixture, into a volume and then polymerizing the lens-forming material to become a solid. The formed lens can be used for ophthalmic or specialty optics applications. Ophthalmic devices have traditionally been created by first forming a cavity out of two separate mold shapes, then filling that cavity with a liquid material that will cure and form a solid shape. The molds used in this type of process are typically glass or metal, based on their high chemical resistance and low amount of geometric distortion they experience over time.
Most commonly, two glass mold pieces and a gasket form the volume that defines the dimensions of the lens to be cast. Some prior art gaskets are known as “T-gaskets,” which include a bore having two ends that each complementarily receives a respective glass mold spaced apart a predetermined axial distance from the other mold. Different T-gaskets are required to form varying power lenses because they only allow one separation distance between molds. Accordingly, manufacturers must maintain T-gaskets for a +2 lens, another for a −3 lens, still another for a −4 lens, etc.
An improvement of this “T-gasket” design is disclosed in U.S. Pat. No. 6,068,464 (hereafter “the '464 patent”), in which at least one of the two molds is slidably movable along the bore of the gasket. This design thus has a “universal” gasket that can be used to form different powers of lenses, whereas a given prior art T-gasket may be used to form one power of lens and a different T-gasket is used to form another power.
U.S. Pat. No. 5,551,663 (hereafter “the '663 patent”) described the use of plastic molds in the manufacture of ophthalmic lenses, but no mention of successfully making lenses is included here. This approach necessitated the use of a “protective coating” first being applied to the mold before the mold could be used. This protective coating became a permanent part of the mold, and allowed for the mold to be used repeatedly. Evidence of the permanence of the coating is apparent in the description of the adhesion test used to assure proper adhesion of the coating to the mold. The patent describes a “plastic mold having an adherent, abrasion resistant, release enhancing face.” The purpose of the coating of the '663 patent is to prevent attack of the mold by the lens material. (By comparison, this current patent application applies a coating to the mold, but with the intent that the coating be only temporary, and that it transfer via chemical or physical bonding to the lens material.)
The method of the '663 patent raises significant issues about its ability to consistently produce high-quality molded lenses. Possible problems that might occur with the method of the '663 patent include a decay in the optical quality of the mold. Any defect on either side of the mold could affect the finished quality of the lens. The decay can take the form of yellowing, cracking, scratching, and physical deformation. These forms of decay can occur with repeated use of a non-rigid material. Any of these types of decay could alter the optical quality of lenses made. Additionally, plastic materials would be difficult to clean, since they are not very chemically resistant, not scratch resistant, and not very resistant to the heat used in many typical processes.
Accordingly, a need exists for durable, low cost plastic molds that can be used to create lenses of various powers.